There are also some airway reporting points which are designated "M" which means you should send an AirRep (usually just spot wind and OAT).
EG Entry/Exit points at Morrocan airspace (High Level) - have a look at the charts.
That said not many seem to bother but personally I always give the Report and they seem to appreciate it - I guess it's a lack of data in these areas is why they want the info and one day you might benefit from the information passed by another a/c?